Incorrect. Having topic or post in your URL will never lower your SEO score... SEO score being itself such an abstract concept, focus on delivering high quality content instead of trying to optimize for silly things like this.

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Thank you all
I just want to change /topic/1234/hello to /topic/1234
How to removing the topic name from the actual page url ?
etc recent or popular pages
If add the url (shorten) custom by admin extend
It's very convenient.

is NodeBB "rendering-and-writing" the "ajaxified" pages for the crawlers to read?
@bentael -- no way, I made the decision early on not to do this because it is a drain on resources (how much, I did not test, as the alternatives were enticing enough)
Every link on NodeBB is accessible by direct link, and if you try viewing the source, you'll see the page content in <noscript> tags. I have heard arguments for and against this approach, but as we are being crawled properly by Google, it seems to be working just fine
Always open to suggestions for improvements, of course!
This is also the approach that Discourse has taken, btw.